Environmental Engineering Reference
In-Depth Information
an excess amount is released into the environ-
ment, contaminating surface waters and causing
eutrophication. The waste/unutilised P from the
animal manure accumulates in the surface soils
and, thereafter, leads to increased leaching and
erosion losses of that P to aquatic environments
(Bohn et al.
2008
). This leaching as “run-off” is
more pronounced in P saturated soils and even
more easy from soils with low retention capac-
ity, e.g. highly organic (especially peat) soils and
sandy soils. P transferred in this way can be ei-
ther in soluble (dissolved) or “attached” (sorbed
to or part of soil inorganic and organic materials)
forms. These losses of P that may not regarded as
significant in agronomic terms can be significant
in environmental terms due to the fact that a very
small concentration (ca. 20 μg/L) in susceptible
surface waters can lead to eutrophic conditions.
It has possible consequences in water use for
fisheries, recreation, industry or drinking due to
the increased growth of algae and aquatic weeds
and oxygen shortages (Bomans et al.
2005
). Ma-
nure-borne P is a serious environmental hazard
that has been reviewed by several researchers
(Centner
2004
; Shigaki et al.
2006
; Powers and
Angel
2008
).
In a survey, Bertrand et al. (
1999
) found that
dairy diets in the USA were formulated with 20 %
more P than the recommended limit released
by NRC (
2001
). This P oversupplementation
(~ 20 %) to the national dairy herd was reported
to cost $ 100 million p.a. and contributed to un-
desirable high manure P levels (Satter and Wu
2001
). According to Wu et al. (
2000
), the extra
P was not needed as no difference in animal per-
formance parameters was reported. A reduction
of 25-30 % in manure P and a saving of $ 10-15/
year-cow could occur with reduction in this P
over supplementation.
column and sediments). External loading of P
in streams and rivers is usually contributed by
anthropogenic processes through nutrient inputs
from the fertilisation of soils, soil erosion, animal
farming waste and disposal of municipal or in-
dustrial effluents, and atmospheric deposition of
P enhanced by emissions (Bomans et al.
2005
).
Internal loading, which is particularly important
in shallow lakes, estuaries and near-shore seas
while less significant in deep lakes and ocean
basins, results from seasonal or annual return to
the water column of nutrients that have sunk and
accumulated in sediments. In general, the effects
of anthropogenic eutrophication are negative,
and the beneficial effects are rare or accidental
(Bomans et al.
2005
). The eutrophication of P in
water bodies may result in a number of conse-
quences in aquatic ecosystems. The potential P
eutrophication of fresh water streams, lakes and
near-coastal areas can cause algal blooms, hy-
poxia and death of aquatic animals followed by
production of nitrous oxide, a potential green-
house gas (Mallin and Cahoon
2003
). The popu-
lation explosions of algal species are called red
tides or algal blooms and their proliferation and
occasional dominance by particular species is
a result of the combination of physical, chemi-
cal and biological mechanisms and interactions.
Algal species have wide differences in their toler-
ance and requirements of nutrients; where some
are tolerant to high levels of P, others are adapted
to low P conditions. The change in nutrients, light
conditions due to high algal growth and oxygen
availability favour growth of some species over
others and cause shifts in the structure of phyto-
plankton and zooplankton, thus altering commu-
nity structure. It may trigger reduced growth and
recruitment of fish species and death of fishes,
causing low fishery production. Moreover, mod-
erate nutrient enrichment can sometimes also
lead to an increase in population of economically
valuable fishes in some ecosystems.
Another consequence of eutrophication is
decreased availability of silica, which diatoms
require to form their glasslike shells. This can
also alter the phytoplankton community by limit-
ing growth of diatoms or causing a shift in other
types of diatoms. Studies off the German coast
7.3.2
Eutrophication and Loss of
Biodiversity
Eutrophication of aquatic systems is further con-
sidered as a result of external loading (nutrient
inputs from outside the aquatic system) and inter-
nal loading (nutrient recycling within the water
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